1. Field of the Invention
This invention relates to the preparation of copolyamides and is particularly concerned with aromatic copolyamides.
2. Description of the Prior Art
Various types of polyamide polymers, and, particularly, aromatic polyamides are well known in the art and are widely employed in a variety of applications. Of particular interest are the aromatic polyamides and copolyamides having high resistance to heat. Unfortunately, many of the wholly aromatic polyamides which do have excellent high temperature resistance are so high melting (&gt;300.degree. C.) as to be unmeltable without decomposition thereby precluding their manipulation by melt processing techniques such as injection molding. Consequently, while the properties of such polymers make them excellent candidates for a number of high temperature applications, their intractability narrows this use considerably.
A number of prior art polymers have been discovered which have solved the melt temperature intractability problem but with a resultant lowering in their high temperature resistance properties. For example, U.S. Pat. Nos. 4,072,665 and 4,087,481 disclose injection moldable copolyamides having good high temperature resistance wherein the combination of certain aliphatic and aromatic diradicals is taken advantage of to achieve these ends.
U.S. Pat. No. 3,505,288 discloses injection moldable aromatic polyamides wherein the --CONH-- carbonamide groups (hereinafter --AB-- wherein the --A and B-- portions represent the --CO and the NH-- respectively) are linked as --AABBAA-- wherein the --BB-- linkages contain particular phenylene ether diradicals and the --AA-- linkages contain arylene diradicals.
U.S. Pat. No. 4,278,786 improves the melt moldability of the types of polyamides disclosed in U.S. Pat. No. 3,505,288 by employing a particular combination of m-phenylene and p-phenylene diradicals in the --AA-- linkages. At the same time, this reference discloses that up to 50 mole percent of the phenylene ether diradicals in the --BB-- linkages can be replaced by other types of arylene diradicals including m-phenylene before melt moldability deteriorates.
Closely related to U.S. Pat. No. 4,278,786 above is Japanese Kokai J56 099228 which discloses similar aromatic polyetheramides wherein 50 to 98 mole percent of the --BB-- linkages contain the phenylene ether diradicals while 2 to 50 percent are based on arylene and/or alkylene diradicals and the --AA-- linkages contain arylene diradicals.
We have now discovered an aromatic copolyamide wherein the randomly linked --AABBAA-- polymer backbone has a majority of the recurring units wherein the --BB-- linkages contain the m-phenylene diradical with only a minor proportion containing a particular phenylene ether diradical. All of the --AA-- linkages contain the m-phenylene diradical.
Surprisingly, even though the all-aromatic polymer backbone is very similar to prior art non-injection moldable aromatic copolyamides, the polymers in accordance with the present invention are injection moldable.
Unexpectedly, the present polymers enjoy a considerably higher heat resistance than the prior art melt moldable copolyamides of the type set forth in U.S. Pat. No. 4,278,786, and Japanese Kokai No. J56 099228, cited supra.